1. Field of the Invention
This invention relates to the treatment of hazardous waste produced by industry, and preferably liquid hazardous wastes.
2. Prior Art
One of the most desirable ways of disposing of hazardous waste chemicals, e.g. radioactive waste, carcinogenic waste, etc., and reducing hazards to acceptable levels, is to solidify such chemicals. Many studies have been made on mixing such hazardous materials with concrete composed of cement, sand and gravel and sometimes other additives to make a solid mass. Such a method poses problems in contamination of the mixing vehicles, spillage and ventilation problems. Additional methods used are to build containers of concrete, steel, glass and combinations thereof to contain such chemicals for an indefinite period. Such methods have proven to have unacceptably high failure rates. To date, concrete encasement is probably the best method. Concrete, however, as presently used in industry has a high percentage of water of hydration leaving little opportunity for the cement fraction to absorb the excess hazardous liquids to immobilize the waste therein, i.e. the high percentage of the water of hydration uses up most of the concrete's ability to absorb liquid.
It is a common practice to process liquid hazardous or radioactive materials by adding absorbants in an attempt to simplify handling and transportation as well as eventual storage thereof. The materials that have been used heretofore include diatomaceous earth, vermiculite or expanded mica such as zonolite and krolite, Portland and Gypsum cements, as well as clay materials such as calcium bentonites. The problem with such materials is that only a relatively small amount of liquid can be absorbed or otherwise treated with less than satisfactory results and complicated mixing equipment is required which becomes contaminated. For example, liquid materials may be transported and disposed of in fifty-five gallon drums. However, it has been found that with the use of these absorbants, solid compositions cannot be achieved or if temporarily achieved, liquid separation occurs during transportation or storage. Any separated or free standing liquids are especially undesirable because of the potential danger of leakage from a ruptured or open container.
The following patents are relevant hereto:
______________________________________ U.S. Pat. No. Inventor ______________________________________ 3,983,050 Mecham 4,116,705 Chappell 4,174,293 Colombo, et al 4,775,494 Rowsell et al. 4,855,083 Kagawa et al. 4,913,835 Mandel et al. ______________________________________
Mecham (U.S. Pat. No. 3,983,050) describes the use of dry cement powder which is added to a metal canister containing dry radioactive calcined wastes so that the cement powder is in contact with the inner surface of the wall of the canister before the canister is sealed. If the container wall fails moisture from the environment contacts the cement and solidifies the cement to thereby seal the wall. In an embodiment the cement is mixed with the dry waste and placed in the metal canister.
Chappell (U.S. Pat. No. 4,116,705) describes a process which comprises treating hazardous waste with (i) an aluminum silicate or an aluminosilicate and (ii) a Portland cement, in the presence of water to form a slurry and allowing the slurry to set into rock and a crystal matrix having encapsulated therein the hazardous waste.
Rowsell et al., (U.S. Pat. No. 4,775,494) discloses the concept of disposing of radioactive or hazardous liquid waste by placing the liquid in a container and adding sodium montmorillonite over intervals until the composition is substantially solid in the container.
Colombo et al. (U.S. Pat. No. 4,174,293) describes a process for disposing of aqueous waste solutions by dispersing the solution in situ throughout a mass of powdered Portland cement in a container, curing the cement and thereafter impregnating the cured cement with a mixture of a monomer and polymerization catalyst and polymerizing the monomer. The container is then appropriately stored.
Kagawa et al. (U.S. Pat. No. 4,855,083) describes a solidifying agent comprising slag dust, silicates, water-soluble, high molecular weight compounds, metal salts of an organic acid and calcium carbonate. The solidifying agent is mixed with organic halogenides, such as PCB, to form solid composites which are subsequently burned.
Mandell et al. (U.S. Pat. No. 4,913,835) teaches spraying a particulate composition containing an organic acid neutralizing agent on a hazardous alkali spill.
Still further, at present, it is generally essential that a cementitious composition is mixed with water before placement in order to moisten the cementitious particles for the start of hydration and lock in place the hazardous waste. Generally, some type of mixing is required. Some manufacturers of premixes, usually in a container having instructions thereon, have put a dry premix cementitious composition in a hole or container and then recommended adding the water on top or through tubes. Some manufacturers have put premixes in bags and dropped the mixes, while in bags, through the water, then after the bags are in place, letting water penetrate through the bag to the mix. However, these systems do not permit full hydration of the cementitious composition. Mortar mixers, concrete mixers and hand mixing have been utilized to obtain a uniform distribution of the appropriate amount of water in the cement. According to the prior art, the quantity of water to be mixed with the cement must be controlled to a very narrow range, and too little or too much water will produce an ineffective or unusable material. Cementitious mixtures could not be placed in a dry state directly into water or on to a wet surface without first wetting and mixing the dry components with water.
In summary, solidification of waste materials with cementitious compositions is known, however, such is accomplished by either mixing the waste material with the cementitious composition to obtain essentially complete hydration or adding the liquid to the cementitious composition with or without mixing. There is no teaching or suggestion in the art of adding the cementitious composition to the hazardous waste without mixing to produce a solidified mass.